November 2010 - Issue #11
Weight loss for healthier cars
Story by Tim Treadgold
View articles in related topics: Automotive Industry, Sustainability & The Environment, Industry Collaboration
Most of us could probably lose weight and live a healthier lifestyle. Well, the same applies to cars because light cars burn less fuel and pollute less. That’s why the ultra-lightweight metal magnesium is seen as having a big role in the future of transport – once a way is found to work with it.
For decades, magnesium has been the metal the car industry wants, but only if scientists can master some of its less attractive properties, such as being prone to galvanic corrosion when joined to other metals, and to cracking when joined by metal-forming processes (for example, clinching, self-pierce riveting). Solving the magnesium riddle would make a significant contribution to pollution reduction, especially carbon dioxide (CO2).
This is why a research team at Swinburne University of Technology is working with industry associates to find a way to join magnesium with aluminium and steel, the two main metals currently used in vehicle construction. And they might have done it – via a combination of lasers, self-piercing rivets and high-strength glue.
Dr Yvonne Durandet, a research engineer and project leader at the Industrial Research Institute Swinburne , says that at room temperature magnesium is not ductile, meaning it lacks the plastic or deforming qualities needed to be pierced and joined by a rivet.
“If the magnesium is at the bottom layer of a joint stack with another metal it can crack during the joining process,” Dr Durandet says. “So our research focus has been on finding a way to heat the magnesium using a laser to eliminate the cracking problem, while also using a high-strength adhesive to strengthen the joint and protect against any possible future corrosion.”
Our partners
Collaborating with Swinburne in the hunt for a magnesium solution is Henrob (a global company that has commercialised Australian riveting technology), Henkel (a specialist in adhesives, sealants and surface treatments) and the CAST Cooperative Research Centre (CAST), which plays a leading role in metals technology, with a research focus on aluminium, magnesium, steel, titanium and cast iron. Other CAST project partners include Deakin and Central Queensland universities.
Each partner in the project has brought their particular expertise in the search for a solution to a problem that has frustrated vehicle makers and held up the development of magnesium as a metal of the future.
Australia, which has vast deposits of magnesium in the ground, came close to developing a world-class magnesium metal production industry in the 1990s. But a combination of low-priced magnesium exports from China, cost over-runs and lack of confidence in the industry at the time saw several local magnesium metal development plans mothballed.
The team at Swinburne believes it is close to resolving the magnesium-joining puzzle by integrating the technologies brought to the table by the different participants.
“We have known for some time that magnesium cannot be easily joined using just self-piercing rivets,” Dr Durandet says. “There is also a problem if you use a fusion (heat) process such as welding because the material properties can change and result in a brittle joint.”
Enter the laser. This tool is used to rapidly spot-heat the magnesium to a temperature that makes the metal more ductile, permitting the insertion of a self-piercing rivet.
Combined with the laser and rivet is the application of an adhesive between the two metals. This serves a dual purpose: it strengthens the joint and acts as a corrosion barrier.
The process has the added advantage of being fast. The laser does its heating job in about two seconds. The joining process takes about another two seconds. On a vehicle production line, time is a critical element.
The breakthrough
The Swinburne team has achieved a joining system that provides the double strength of riveting and adhesion, with each step complementing the other. The rivet provides spot-joining. The adhesive provides a continuous joint and also the protective barrier needed between two different metals.
The benefits of making magnesium an easier metal for the vehicle industry to use are substantial. Reducing the weight of cars and trucks is a key to using less fuel and that means a reduction in pollution.
Vehicles that emit the lowest levels of CO2 are not just those using electrically assisted hybrid engines, they are cars with the lowest weight. The petrol-driven Smart car, for example, achieves a lower level of CO2 emission than well-known hybrids largely because it is one of the lightest cars on the market. Light-weighting is also important for extending the range of electric vehicles.
The Swinburne-led laser-assisted self-pierce riveting research breakthrough is not yet used in car production, but talks are under way with vehicle makers and original equipment manufacturers. “CAST has licensed the technology to Henrob in the belief that there are major vehicle makers keen to make greater use of magnesium,” Dr Durandet says.
Given the pressure on vehicle makers to cut overall fuel consumption, especially in the US and Europe where strict new rules are being introduced, it is highly likely that magnesium will finally find a leading role in car production. When that is achieved the work at Swinburne and CAST will be seen to have been instrumental in achieving a major environmental improvement.
